854 



SCIENCE 



[N. S. Vol. XLIV. No. 1146 



like the taste of crab juice in the ease of 

 Metridium mentioned by Professor Grave, 

 cause its acceptance, or perhaps its rejection? 

 He says only that food particles, and not that 

 sand or other matter in suspension, cause the 

 reversal that results somehow in the selection 

 of something, either food or material not use- 

 ful as food, it is difficult to determine which. 

 I judge that some diatoms are rejected, and 

 that other diatoms, and sand, are selected. 

 Bhizosolenia, " abundant in salt water, are 

 seldom found in the digestive tract of the 

 oyster." They are not excluded on account of 

 their spiny structure, we are told, because their 

 size is not sufficiently great to prevent their 

 being carried by cilia currents or entering 

 the mouth. Has Professor Grave made ob- 

 servations to determine whether their spiny 

 structure or size is great enough to cause their 

 rejection by the outgoing tracts that, up to this 

 time, I had supposed I had seen in a very great 

 many instances ? I must say that I have not, 

 myself, in the case of this particular diatom; 

 but I have seen certain other diatoms excluded, 

 though not in the oyster. 



And according to this view, it seems neces- 

 sary to assume that sand is selected and sent 

 into the mouth, for Professor Grave tells us 

 that it is a " fact that the stomach contents 

 of oysters always contain a larger volume of 

 sand than of food organisms." I am grateful 

 to him for adding that this is difficult to ex- 

 plain on the Kellogg theory. I am sure that 

 he will not contend that everywhere, where 

 oysters and other lamellibranchs " thrive," 

 suspended sand is in greater volume than sus- 

 pended diatoms. "When it is not, do oysters 

 select sand, and reject diatoms that are suitable 

 for food? They must do the one thing or the 

 other, or both, if sand is always to be more 

 abundant than diatoms in their stomachs. It 

 is difficult to understand how statements of 

 this sort can so easily and confidently be made, 

 and this one indicates how limited have been 

 Professor Grave's studies on the stomach con- 

 tents of oysters, to say nothing of those of 

 other lamellibranchs. My own study of this 

 subject has not been extensive, either, but I 

 have material on hand to disprove this state- 



ment, if it is applied to the group of lamelli- 

 branchs in general. My "theory," that has" 

 been attacked, does not apply to the oyster 

 alone, but to all lamellibranchs, most of which 

 demonstrate it more clearly than the oyster 

 does. 



What may be called the argument of Pro- 

 fessor Grave concerning the supposed reversal 

 of the cilia beat on the palp tracts, with results 

 that he makes no pretence of having observed, 

 and has not formulated in his own mind, is 

 based on the statement of Engelmann that 

 he has actually witnessed this reversal on the 

 palps of lamellibranchs, and on the facts that 

 a reversal occurs in Stentor and other protozoa, 

 and in Metridium, resulting in the selection of 

 food and in the rejection of other particles. 



I do not feel that I am in a position to ob- 

 ject that even one who has never studied the 

 matter himself should, without any question 

 or hesitation, accept the statement of Engel- 

 mann and reject my own, on the matter of 

 cilia reversal on the lamellibranch palp. 

 "Why then," asks Professor Grave, after 

 quoting Engelmann, " if a reversal of cilia and 

 selection of food takes place in lamellibranchs, 

 did Dr. Kellogg fail to see the reversal proc- 

 ess ? " The matter is settled at once ; but I 

 venture to suggest that somebody else should 

 examine the palps of Schizotherus, of some 

 species of Cardium, and of some other lamelli- 

 branchs in which the palp folds are large, to 

 see what he can find. Let him be warned that 

 he has no simple task, to be decided by a few 

 observations. The turmoil on the palp face is 

 so extraordinarily confusing that it seems just 

 possible that even Engelmann may have been 

 mistaken. I have supposed that I also have 

 seen a reversal of the cilia beat on the palp, 

 but many years ago concluded that I was mis- 

 taken. It is entirely possible that my present 

 belief is erroneous, but I would prefer to be 

 corrected by some one who has at least made 

 an effort to study a few lamellibranchs, in- 

 stead of studying papers. That protozoa re- 

 verse the cilia beat adaptively in food selec- 

 tion is suggestive in this ease; but protozoa 

 are not lamellibranchs, and I had hoped that 

 the argument from analogy had been aban- 



